1. Field of the Invention
The present invention relates to a sensor device configured to convert a physical quantity (for example, magnetic field intensity) into an electric signal, and more particularly, to a magnetic sensor device to be used for, for example, an open/close state detection sensor for a flip cell phone or a notebook computer, or a rotation number/rotation position detection sensor for a motor.
2. Description of the Related Art
A magnetic sensor device has been used for an open/close state detection sensor for a flip cell phone or a notebook computer, or a rotation number/rotation position detection sensor for a motor.
The magnetic sensor device outputs a voltage proportional to magnetic field intensity or magnetic flux density by a magnetoelectric conversion element (for example, Hall element), amplifies the output voltage by an amplifier, and determines the amplified voltage by a comparator, thereby outputting the determined voltage as a binary value of an H signal or an L signal. Because the output voltage of the magnetoelectric conversion element is minute, an offset voltage of the magnetoelectric conversion element (element offset voltage), an offset voltage of the amplifier or the comparator (input offset voltage), or noise generated in the magnetic sensor device causes a problem. The element offset voltage is generated mainly by stress on the magnetoelectric conversion element received from a package. The input offset voltage is generated mainly by characteristic fluctuations in elements forming an input circuit of the amplifier. The noise is generated mainly by flicker noise of a single transistor forming the circuit or thermal noise of a single transistor or a resistive element.
In order to reduce the fluctuations in magnetic detection/release operation, which occur due to the above-mentioned noise of the magnetoelectric conversion element and the amplifier, without significantly increasing power consumption, a magnetic sensor device illustrated in FIG. 10 has been proposed (for example, see Japanese Patent Application Laid-open No. 2013-74415).
The related-art magnetic sensor device includes a Hall element 1 being the magnetoelectric conversion element, a switching circuit 2, a differential amplifier 3, a comparator 4, a control circuit 5, D type flip-flops D1, D2, and D3, XOR circuits X1 and X2, selector circuits SL1 and SL2, an AND circuit AN1, an OR circuit OR1, a capacitor C1, a switch S1, an output terminal VOUT, and terminals E1 and E2. The logic circuit successively verifies logic outputs a plurality of times only in a case where the logic outputs are changed due to change in magnetic field intensity.
However, the related-art magnetic sensor device always makes magnetic determination, which requires a constant signal processing period and thus has high accuracy, even when a mobile device is normally used (for example, a flip cell phone is in a fully opened state or a fully closed state) and an applied magnetic field hardly changes. Consequently, an effect of reducing average current consumption is limited.